View, add, or subtract credits for a member.
Go to Members → click on the member's name.
Their credit balance is a chip in the header ("4 credits"), and the "Class credits" card is on the Money tab. The quickest route is "Add credit" in the row of buttons under their name — it opens the same box from wherever you are on the page.
Click "Adjust Credits". Enter the amount to add or subtract, and optionally a note explaining why.